Using once piece of Marres response: "Or undead murkgliders in Noble's Causeway--they hit hard, again, but it's possible to solo them if you can kite them somehow or if you have a healer merc possibly." basically sums up why knowing what specific class does matter.
As a kiter, the undead murks are a ridiculously good solo camp for a long time. Pretty much useless to a solo melee in my view.
A zone that hasn't been mentioned is
Halls of Betrayal which is a really good (if not fantastic zone) of non-runners. For xp purposes it's good because you get yourself down there and stay there until you are done. It's recommended 53-63 so it covers part of the range said by the OP in the OP.
Crypt of Nadox is listed as 50-65 so clearly meets the query of the OP.
The other posters here (not me, I don't know high level stuff) can give very precise and insightful answers when they know the specifics.
Example:
Soloing a warrior without mercs vs. non-runners (so pretty much undead) from 58-68 is a totally different situation than some sort of PLing involving an 80 or 85 character --which is kind of what the 3rd post implies.
edit: spelling
Edited, Feb 23rd 2011 9:22pm by snailish